Find a song that is very popular. Making a parody out of a song is not much fun if nobody knows the song but you. Take your time and listen to the radio to see what songs are played the most. This will give you a good idea as to which songs to work with.
Listen to the song and find a topic that you would like the parody to be about. Listen to a Weird Al CD and you will have a better idea of what a parody is and how it should sound.
Develop the parody. This could take some time because you will need to make sure it sounds just like you had imagined it would. Use all your creativity to create the parody that you want.
Get permission from the artist of the original song if you plan to take the parody any further, such as releasing it for the public to hear, placing it on a CD, or making an entire CD of parodies.
Make as many parodies as you can and pick the best ones for your recordings. Your friends will have a good time listening to your work.